Radiocarbon dating rock art
Pictographs are made through an additive process, where they are applied to the rock surface, and include paintings, charcoal drawings, stencils, prints.
Petroglyphs are made by a reductive process, in which they are cut into the rock by engraving, pecking, incising or abrasion.
This may be the result of differential preservation as most of Nevada's pictographs are situated inside caves, rock shelters or other contexts, which afforded some measure of protection from the elements.
This biased distribution does suggest that potentially many more pictographs existed in the past in unsheltered contexts, but these have simply weathered away and did not survive into present.
Archeologists can determine the age of a charcoal sample by measuring its carbon content.
Though the science of radiocarbon dating was greatly advanced by the advent of accelerator mass spectrometry, which can evaluate the age of even minute samples of charcoal, dating rock art is still problematic.
Very few rock art sites offer thematic indicators of their age, such as the depiction of extinct animals, or the portrayal of diagnostic artifacts which forms the basis for identifying historic period rock art (for example the portrayal of wagons, people wearing cowboy hats and riding horses, etc.).
Most sites can not be convincingly dated from a consideration of the imagery represented and so a means of directly dating rock art by scientific methods is the subject of intense research.
These types are present in Nevada, but are rare compared to the petroglyphs and pictographs, which are the state's most common types of rock art.Many Native Americans believe that their ancestors were created here at the beginning of time, but most archaeologists agree that people have lived in Nevada for at least 10,000-12,000 years.Of the pictographs and petroglyphs that are found in Nevada, petroglyphs are by far the more common of the two.Accelerator mass spectrometry (AMS) allows archeologists to avoid doing much damage to the rock art they wish to date, since it is able to determine the age of very small amounts of charcoal.
However, in an effort to keep damage to rock art to a minimum, archeologists sometimes take samples of pigment that are so small they do not contain enough charcoal to date.Most fall within the earliest phase of the Formative period, the Mesilla phase, and others fall within the transitional, or Dona Ana phase, the time of the Hueco Tanks villagers.